Isotopic separation of helium through graphyne membranes: A ring polymer molecular dynamics study

11 pags., 7 figs.Microscopic-level understanding of the separation mechanism for two-dimensional (2D) membranes is an active area of research due to potential implications of this class of membranes for various technological processes. Helium (He) purification from the natural resources is of particular interest due to the shortfall in its production. In this work, we applied the ring polymer molecular dynamics (RPMD) method to graphdiyne (Gr2) and graphtriyne (Gr3) 2D membranes having variable pore sizes for the separation of He isotopes, and compare for the first time with rigorous quantum calculations. We found that the transmission rate through Gr3 is many orders of magnitude greater than Gr2. The selectivity of either isotope at low temperatures is a consequence of a delicate balance between the zero-point energy effect and tunneling of 4He and 3He. In particular, a remarkable tunneling effect is reported on the Gr2 membrane at 10 K, leading to a much larger permeation of the lighter species as compared to the heavier isotope. RPMD provides an efficient approach for studying the separation of He isotopes, taking into account quantum effects of light nuclei motions at low temperatures, which classical methods fail to capture.Y. V. S. and S. B. acknowledge the support of the European Regional Development Fund and the Republic of Cyprus through the Research Promotion Foundation (Projects: INFRASTRUCTURE/ 1216/0070 and Cy-Tera NEA YPODOMH/STPATH/0308/31). Y. V. S. was also supported by the Russian Foundation for Basic Research grant number 20-03-00833. J. C.-M. and M. I. H. were supported by Spanish MICINN with Grant FIS2017-84391-C2-2-P and PID2020- 114957GB-I00. We are also indebted to ‘‘Centro de Supercomputacio´n de Galicia’’ (CESGA) and specially to the people in the help desk